This invention relates to a method and apparatus for diverting and sensing a sample portion from a main channel stream of flowing fluid. More particularly, it relates to a method and apparatus for withdrawing a sample portion from a conduit stream of air having an undetermined moisture content which sampling is effected by means of a reduction of pressure to effect flow from the stream to a humidity sensor and return of the sample to the stream. The reduction of pressure to effect the sample flow is effected in a manner such that large particles of moisture or dirt are not drawn into the sensing device.
Sampling devices of the type concerned with in this invention are described in U.S. Pat. Nos. 2,452,224 and 2,475,857. Both of these prior art sampling devices utilize intake tubes or pipes with the orifices facing upstream of the flow of fluid to be sampled. In U.S. Pat. No. 2,452,224, two conduits or tubes are utilized with at least one of their orifices facing fluid flow. These types of arrangements can pose problems in that large particles of moisture and dirt can enter into the sampling system and cause inaccurate readings. If filters are employed, adjustement for undue and undesirable pressure drops across the sampling system must be effected.
It is an advantage of the present invention to provide a noval process and apparatus for diverting and sensing a sample portion from a mainstream of flowing fluid. Other advantages are a method and apparatus for determining the end point for drying wherein the main channel stream is the exhaust air from a drying oven; a diverting and sensing method and apparatus which is particularly suitable for being utilized with a humidity sensor; a method and apparatus for sensing moisture in an air stream which avoids contact or large particles of moisture and dirt with the sensing device; an air sampling device which is simple in its construction, involving a minimum number of parts and readily adaptable to an air flow pipe or conduit.